This project aims to characterize and to determine the prevalence of three virus-like particles (VLP) previously detected by electron microscopy in Spiroplasma citri and now found in three other Mollicutes (Mycoplasmas) now recognized as spiroplasmas (i.e., corn stunt organism (CSO); sex-ratio organism (SRO) of Drosophila; and suckling mouse cataract agent (SMCA). The VLP are (1) SVC1, a rod-shaped particle: (2) SVC2, a long-tailed phage-like particle; and (3) SVC3, a short-tailed particle. S. citri contains all 3 VLP; CSO and SRO contain 2 VLP each (SVC1 plus SVC3); and SVC3 only was found in SMCA. Optimal methods were developed for plaque (infectious center) formation on agar lawns of S. citri by SVC3--from both S. citri and SMCA cultures as virus sources. Titers of 1 x 10 to the 9th power plaque-forming units (PFU)/ ml. can be obtained. Purification methods, being investigated, will permit biological and physicochemical characterizations of this new